Gabriele Cosmo
91 lines
2.7 KiB
Plaintext
91 lines
2.7 KiB
Plaintext
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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field05 Example
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---------------
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This example checks so-called "spin-frozen" condition
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There is a good example article hep-ph/0012087v1.
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This article discusses about how to cancel the muon g-2 precession by
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applying an electric field.
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1) beta is muon velocity,
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2) B is an uniform magnetic field and \vec{beta}.\vec{B}=0,
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"." means scalar product,
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3) Radial electric field (E) in the lab frame and \vec{beta}.\vec{E}=0,
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4) a=(g-2)/2 is muon anomalous magnetic moment.
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The required electric field to cancel the g-2 precession is,
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E=a*B*light_c*gamma**2*beta.
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In case of gamma=5 and B=0.24 Tesla, the required electric field is
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E=2 MV/m.
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"Spin-frozen" happens when spin rotation cycle and muon rotation cycle
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are same. In this case, both cycles should be 149.5 nsec.
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See also:
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http://research.kek.jp/people/hiromi/MyHomePage/G-2_work_files/SpinStudyinEMfieldByGeant4.pdf
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Credit goes to Hiromi Iinuma from KEK
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**************
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*Classes Used*
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**************
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1 - main()
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See field05.cc.
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2- GEOMETRY DEFINITION
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as simple world G4Box with a G4ElectroMagneticField
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propagating both spin and momentum (G4EqEMFieldWithSpin)
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with G4ClassicalRK4(fEquation,12) and
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Bz = 0.24*tesla;
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Er = 2.113987E+6*volt/m;
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3- AN EVENT: THE PRIMARY GENERATOR
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use mu+ G4ParticleGun with Pmu = 517.6*MeV/c
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and aligned spin and momentum direction
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4- PHYSICS
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RegisterPhysics(new G4DecayPhysics());
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RegisterPhysics(new G4StepLimiterPhysics());
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G4VModularPhysicsList::ConstructParticle();
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and replace muon decay modes with those with spin:
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G4MuonDecayChannelWithSpin
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G4MuonRadiativeDecayChannelWithSpin
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and replace G4Decay with
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G4DecayWithSpin process for the muon
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G4PionDecayMakeSpin process for the pion
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G4StepLimiterPhysics defines G4StepLimiter and G4UserSpecialCuts
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5- User Action Classes
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SteppingAction:
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G4Exception when the cosine of the angle between
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the spin and the momentum is < (1.-1.E-7)
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6- HOW TO START ?
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- execute field05 in 'batch' mode from macro files e.g.
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% field05 field05.in > field.out &
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- execute field05 in 'interactive' mode with visualization e.g.
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% field05
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....
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Idle> type your commands, for example:
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Idle> run/beamOn 1
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....
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